Rapid screening of aminopeptidase N inhibitors by capillary electrophoresis with electrophoretically mediated microanalysis

Advances in enzyme substrate analysis with capillary electrophoresis

Capillary electrophoresis provides a rapid, cost-effective platform for enzyme and substrate characterization. The high resolution achievable by capillary electrophoresis enables the analysis of substrates and products that are indistinguishable by spectroscopic techniques alone, while the small volume requirement enables analysis of enzymes or substrates in limited supply. Furthermore, the compatibility of capillary electrophoresis with various detectors makes it suitable for KM determinations ranging from nanomolar to millimolar concentrations. Capillary electrophoresis fundamentals are discussed with an emphasis on the separation mechanisms relevant to evaluate sets of substrate and product that are charged, neutral, and even chiral. The basic principles of Michaelis-Menten determinations are reviewed and the process of translating capillary electrophoresis electropherograms into a Michaelis-Menten curve is outlined. The conditions that must be optimized in order to couple off-line and on-line enzyme reactions with capillary electrophoresis separations, such as incubation time, buffer pH and ionic strength, and temperature, are examined to provide insight into how the techniques can be best utilized. The application of capillary electrophoresis to quantify enzyme inhibition, in the form of KI or IC50 is detailed. The concept and implementation of the immobilized enzyme reactor is described as a means to increase enzyme stability and reusability, as well as a powerful tool for screening enzyme substrates and inhibitors. Emerging techniques focused on applying capillary electrophoresis as a rapid assay to obtain structural identification or sequence information about a substrate and in-line digestions of peptides and proteins coupled to mass spectrometry analyses are highlighted.

Transverse diffusion of laminar flow profiles as a generic capillary electrophoresis method for in-line nanoreactor mixing: Application to the investigation of antithrombotic activity

Capillary electrophoresis (CE) instrument was used for the generation of a robust and reliable nanoreactor for enzymatic assays in the context of antithrombotic drug screening. The activity of the screened molecules was monitored in a quick and fully automated fashion using only few nanoliters of reactants. To achieve this goal, the targeted enzyme (thrombin) and the chromogenic substrate with or without the screened inhibitor were injected as separate plugs. The mixing of the reactants was then realized using electrophoretically mediated microanalysis (EMMA) or fast transverse diffusion of laminar flow profiles (TDLFP) procedure. The latest provided better mixing performance and was chosen to investigate the inhibitory potency of a fragment library. This very straightforward and fast CE activity assay showed results in good accordance with a previously developed CE affinity assay that confirms the potential of CE at the early stages of drug discovery, providing not only an efficient nanoscale bioreactor but also a selective and integrated separation device.

LJNK, an indoline-2,3-dione-based aminopeptidase N inhibitor with promising antitumor potency

In our previous study, we found that LJNK showed potent aminopeptidase N (APN)-inhibitory activity. In the current study, we further evaluated the antitumor effects of LJNK both in vitro and in vivo. Enzyme experiments showed that LJNK showed better inhibitory activity than bestatin against APN both from human carcinoma cells' surface and from porcine kidney microsomes. In addition, LJNK could suppress rat aortic ring microvessel growth and HUVEC tubular structure formation, which showed its stronger antiangiogenesis effects than bestatin. [(3-[4,5-Dimethyl-2-thiazolyl]-2,5-diphenyl-2H-tetrazolium bromide)] assay and clonogenic assay showed that LJNK suppressed cancer cell growth both in the short and the long term. Mice bearing H22 transplantation tumor proved its antitumor effects in vivo. Annexin V-fluorescein isothiocyanate/propidium iodide assay showed that LJNK could induce 28.1% PLC/PRF/5 cell apoptosis and the apoptotic pathway was probably identified by western blot. The above-mentioned results suggested that LJNK inhibited cell proliferation and angiogenesis, and induced apoptosis by decreasing APN activity.

Advances in capillary electrophoresis and the implications for drug discovery

INTRODUCTION

Many screening platforms are prone to assay interferences that can be avoided by directly measuring the target or enzymatic product. Capillary electrophoresis (CE) and microchip electrophoresis (MCE) have been applied in a variety of formats to drug discovery. CE provides direct detection of the product allowing for the identification of some forms of assay interference. The high efficiency, rapid separations, and low volume requirements make CE amenable to drug discovery. Areas covered: This article describes advances in capillary electrophoresis throughput, sample introduction, and target assays as they pertain to drug discovery and screening. Instrumental advances discussed include integrated droplet microfluidics platforms and multiplexed arrays. Applications of CE to assays of diverse drug discovery targets, including enzymes and affinity interactions are also described. Expert opinion: Current screening with CE does not fully take advantage of the throughputs or low sample volumes possible with CE and is most suitable as a secondary screening method or for screens that are inaccessible with more common platforms. With further development, droplet microfluidics coupled to MCE could take advantage of the low sample requirements by performing assays on the nanoliter scale at high throughput.

Methionyl-Methionine Promotes α-s1 Casein Synthesis in Bovine Mammary Gland Explants by Enhancing Intracellular Substrate Availability and Activating JAK2-STAT5 and mTOR-Mediated Signaling Pathways

BACKGROUND

Interest is increasing in the role of peptide-bound amino acids (AAs) in milk protein synthesis because studies have found that the uptake of some essential AAs by the mammary gland cannot meet the requirements for milk protein synthesis. Although the role of dipeptides in milk protein synthesis is clearly established, little is known about the underlying mechanisms.

OBJECTIVE

The objective of this study was to determine whether small peptides can be taken up intact by the peptide transporters in mammary tissue explants and the underlying mechanisms of the effects of methionyl-methionine (Met-Met) supplementation on milk protein synthesis.

METHODS

Mammary tissue explants were cultured in conditional medium and then treated with different concentrations of Met-Met that replaced 0%, 5%, 10%, 15%, 20%, and 25% of free Met for another 24 h. In some experiments, explants were cultured with an optimal dose of Met-Met with or without the inhibitors of peptide transporter 2 [PepT2; diethylpyrocarbonate (DEPC), 0.1 mmol/L] and aminopeptidase N (APN; bestatin, 20 μmol/L) for 24 h.

RESULTS

The substitutions of 15% free Met with Met-Met significantly promoted α-s1 casein (αs1-CN) expression in the mammary explants (P < 0.05). The inhibition of the PepT2 by DEPC or APN by bestatin significantly decreased the Met-Met-stimulated increase of αs1-CN expression (P < 0.05). Compared with the control group (0% Met-Met), absorption of Val, Met, Leu, Phe, Lys, and His was improved, and mRNA abundance of the neutral and basic AA transporter was increased in the 15% Met-Met group (P < 0.05). In addition, the mRNA abundance of the mammalian target of rapamycin (mTOR), p70 ribosomal S6 kinase 1 gene, eukaryotic initiation factor 4E binding protein 1 gene , Janus kinase 2 (JAK2), and signal transducer and activator of transcription 5 (STAT5) was increased in the 15% Met-Met-treated group (P < 0.05).

CONCLUSION

Met-Met promoted αs1-CN synthesis in cultured bovine mammary gland explants, and this stimulation may be mediated by enhanced intracellular substrate availability and by activating JAK2-STAT5 and mTOR signaling pathways.